See the code fragment... the panel Header loads the Ext.draw.Component.

The draw.Component requires pretty much the entire draw package. It loads both engines: VML and SVG, and it doesn't event check if the engine is supported. This is a ton of code, see this open ticket (http://www.sencha.com/forum/showthread.php?130546-OPEN-EXTJSIV-1401-Ext.draw-loads-unsupported-engines).

I suggest adding conditional resource loading or even creating two header types: Vertical and Horizontal.